The field of planar integrated optical photodetector for telecommunication in the near IR band has generally utilized germanium (Ge) as an absorption layer, due at least in part, to the large absorption coefficient of Ge at the near IR wavelengths. Si is transparent at these IR wavelengths and generally unsuitable for use as a photodetector in such applications.
The paper “Germanium Avalanche Receiver for Low Power Interconnects,” Nature Communications 5, Article number: 4957, by Leopold Virot et al., discloses a waveguide avalanche Ge photodiode capable of detection at 10 Gbit per second under low bias conditions. A lateral Ge PIN diode is described that has a thin (500 nm) Ge multiplication region and a Ge absorption region. Efficient butt-coupling was demonstrated by directly connecting the Si waveguide to the Ge absorption region. The dark current increases to 610 uA at −7V bias in avalanche conditions. The quality of the Ge crystal grown was verified by a low value of the dark current at low bias conditions, i.e. 18 nA at −1V bias.
The paper “Silicon Optical Interconnect Device Technologies for 40 Gb/s and Beyond,” IEEE Journal of Selected Topics in Quantum Electronics, Vol. 19, No. 2, March/April 2013 by Tsung-Yang Liow et al., discloses that a lateral Ge PIN avalanche detector has a significant increase in dark current after being stressed for 15 minutes at a reverse bias of −9V, compared to a pristine unstressed device. The cause is believed to be related to mid-bandgap states which may be located at the Ge to cladding oxide interface. Some partial recovery was also observed.
There is a desire to limit the increase in dark current due to the application of an initial high reverse bias voltage for an avalanche photodiode.